Delete duplicate Matomo Tag Manager comment

Author: stevepiercy

docs/_templates/layout.html

@@ -2,7 +2,6 @@
 {%- block extrahead %}
 {{ super() }}
 <!-- Matomo Tag Manager -->
-<!-- Matomo Tag Manager -->
 <script>
 var _mtm = window._mtm = window._mtm || [];
 _mtm.push({'mtm.startTime': (new Date().getTime()), 'event': 'mtm.Start'});